(1) Field of the Invention
This invention relates to lead acid storage batteries. In particular, it relates to a composition of matter useful for the grids of such batteries.
(2) Description of the Prior Art
The basic structural material from which the vitals of lead acid storage batteries are built is lead. Pure lead is a very soft and ductile material. From the beginning of the storage battery industry, ways have been sought to increase the strength and the stiffness of lead so as to improve the battery and to permit its manufacture by mechanical means. Antimony added to lead has a remarkable strengthening effect. It is the classical lead hardening agent and lead antimony alloys have been almost universally used for battery parts. Unfortunately, antimony has also been found to be a sort of chemical poison for lead acid storage batteries.
The deleterious effects of antimony are well documented as are the efforts of the storage battery industry to find alloys that have strength approaching the antimony alloys without the deleterious side effects. A great many alloys of lead have been made and tested for use in storage batteries. At least 14 elements from the Periodic Table have been used to alloy with lead either as binary, tertiary or quaternary alloys. One such alloy consists of lead plus a small quantity of calcium. This alloy, though not as strong as the lead antimony alloys, is strong enough to meet many requirements and is completely free of any poisoning effects. Lead calcium alloys therefore are assuming increasing importance in the storage battery industry. Unfortunately, this alloy has some faults of its own. It is a difficult material to cast and in order to fill out a mold, the metal must be handled at high temperatures. Under high temperature conditions, the calcium rapidly oxidizes from the molten metal and thus careful controls are required to maintain the metal composition. Moreover, it has been found that lead calcium alloys are subject to a form of intergrannular corrosion when subjected to the conditions found in the positive grid of a storage battery. Because of this, batteries using lead calcium grid alloy often do not give as long a life as they should from theory. Often it is found that a lead antimony cell in practice will give as good life as the lead calcium. It has been found that the size of the grains found in lead calcium alloy castings relates to the corrosion effect and the industry tries to control the grain size although this is a difficult and expensive producing exercise.
Lead zinc tin alloys are known as soldering material for aluminum as well as a coating material for steel.